Magnetic resonance imaging method and apparatus

Abstract

A magnetic resonance imaging method for emitting a single excitation RF pulse and then a plurality of refocusing RF pulses to an examinee to generate echo signals successively. This method includes the steps of emitting the single excitation RF pulse and then the plurality of refocusing RF pulses to the examinee to generate echo signals successively; applying slice selecting gradient field pulses for selecting a slice plane simultaneously with the excitation RF pulse and the refocusing RF pulses; applying phase encoding gradient field pulses for phase-encoding a key echo signal and subsequent echo signals among the echo signals resulting from the above steps, without applying the phase encoding gradient field pulses for phase-encoding echo signals generated before the key echo signal, the key echo signal being a signal having collected data of lines in and adjacent a center region of a raw data space of the slice plane; and applying reading gradient field pulses in respect of the echo signals for which the phase encoding gradient field pulses have been applied.

What is claimed is: 
     
       1. A magnetic resonance imaging method for emitting a single excitation RF pulse and then a plurality of refocusing RF pulses to an examinee to generate echo signals successively, said method comprising the steps of: (a) emitting said single excitation RF pulse and then said plurality of refocusing RF pulses to the examinee to generate echo signals successively;   (b) applying slice selecting gradient field pulses for selecting a slice plane simultaneously with said excitation RF pulse and said refocusing RF pulses;   (c) applying phase encoding gradient field pulses for phase-encoding a key echo signal and subsequent echo signals among the echo signals resulting from steps (a) and (b) above, without applying the phase encoding gradient field pulses for phase-encoding echo signals generated before said key echo signal, said key echo signal being a signal having collected data of lines in and adjacent a center region of a raw data space of said slice plane; and   (d) applying reading gradient field pulses in respect of the echo signals for which said phase encoding gradient field pulses have been applied.   
     
     
       2. A method as defined in claim 1, wherein, at step (a), an "n"th refocusing RF pulse, "n" being a positive integer is emitted at a point of time after emission of said excitation RF pulse, expressed by {2(n-1)+1}τ, where τ is a point of time at which a first excitation RF pulse is emitted. 
     
     
       3. A method as defined in claim 1, wherein said key echo signal at step (c) is an echo signal occurring upon lapse of 60 to 120 msec after emission of said excitation RF pulse. 
     
     
       4. A method as defined in claim 1, wherein said key echo signal and subsequent echo signals are phase-encoded at step (c) such that the greater phase encoding is effected for the later echo signal. 
     
     
       5. A method as defined in claim 1, wherein step (c) includes a step of applying rewind pulses having the same strength and pulsewidth as and a polarity reversed from said phase encoding gradient field pulses, said rewind pulses being applied symmetrically to said phase encoding gradient field pulses about centers of said key echo signal and subsequent echo signals. 
     
     
       6. A magnetic resonance imaging apparatus having a main magnet for generating a uniform static magnetic field in a photographic space in which an examinee is placed, a gradient field coil for generating slice selecting gradient field pulses, phase encoding gradient field pulses, and reading gradient field pulses having field strengths varying in three-dimensional directions perpendicular to one another in the static magnetic field, and an RF coil for emitting an excitation RF pulse to the examinee and detecting echo signals from the examinee, said apparatus comprising: RF pulse emitting means for emitting a single excitation RF pulse and then a plurality of refocusing RF pulses successively with predetermined timing through said RF coil, an "n"th refocusing RF pulse ("n" being a positive integer) being emitted at a point of time after emission of said excitation RF pulse, expressed by {2(n-1)+1}τ, where τ is a point of time at which a first excitation RF pulse is emitted;   slice selecting gradient field pulse generating means for generating gradient field pulses through said gradient field coil to select a slice plane, in synchronism with emission of said excitation RF pulse and said refocusing RF pulses;   phase encoding gradient field pulse generating means for generating phase encoding gradient field pulses through said gradient field coil synchronously with a key echo signal and subsequent echo signals, without generating the phase encoding gradient field pulses before generation of said key echo signal, said key echo signal being a signal having collected data of lines in and adjacent a center region of a raw data space of said slice plane, said phase encoding gradient field pulses effecting the greater phase encoding for the later echo signal; and   reading gradient field pulse generating means for generating reading gradient field pulses through said gradient field coil synchronously with said echo signals.